The present invention relates to a variable displacement compressor used in a vehicular air conditioner.
Japanese Laid-Open Patent Publication No. 6-288347 discloses such a variable displacement compressor.
As shown in FIG. 12, the compressor of the publication includes a housing 101, in which a crank chamber 102 is defined. A drive shaft 103 is rotatably arranged in the crank chamber 102. A rotor 104 is coupled to the drive shaft 103 and is located in the crank chamber 102. The rotor 104 rotates integrally with the drive shaft 103. A drive plate, which is a swash plate 105 in this embodiment, is accommodated in the crank chamber 102. A spherical sleeve 106 is slidably supported by the drive shaft 103. The swash plate 105 is tiltably supported by the spherical sleeve 106.
Cylinder bores 101a are defined in the housing 101. Each cylinder bore 101a accommodates a piston 107. Each piston 107 is coupled to the swash plate 105 with a couple of shoes 108. A valve plate assembly 109 is provided in the housing 101. In each cylinder bore 101a, a compression chamber 110 is defined by the associated piston 107 and the valve plate assembly 109.
A hinge mechanism 111 is located between the rotor 104 and the swash plate 105. The swash plate 105 is coupled to the rotor 104 with the hinge mechanism 111 and is supported by the drive shaft 103 with the spherical sleeve 106. This permits the swash plate 105 to rotate integrally with the rotor 104 and the drive shaft 103, and to slide along the axis L of the drive shaft 103. While sliding, the swash plate 105 inclines relative to the drive shaft 103 about the spherical sleeve 106.
As the pressure in the crank chamber 102 varies, the difference between the pressure in the crank chamber 102 and the pressure in the compression chambers 110 is changed. Accordingly, the inclination angle of the swash plate 105 is changed. As a result, the stroke of each piston 107, or the compressor displacement, is varied.
The hinge mechanism 111 includes support arms 112 projecting from the rotor 104 and guide pins 113 projecting from the swash plate 105. A guide hole 114 is formed in each support arm 112, and a spherical portion 113a is formed at the distal end of each guide pin 113. The spherical portion 113a of each guide pin 113 is fitted in the guide hole 114 of the corresponding support arm 112 and slides with respect to the guide hole 114. Each guide hole 114 is parallel to an imaginary surface defined by the axis L of the drive shaft 103 and the top dead center corresponding position of the swash plate 105 (or the center of an imaginary sphere formed by the shoes 108 of the piston 107 located at the top dead center position). Each guide hole 114 is also formed straight toward the axis L of the drive shaft 103.
Therefore, when the inclination angle of the swash plate 105 increases, the spherical portion 113a of each guide pin 113 is rotated clockwise as viewed in the drawing about an axis P, which extend through the center of the spherical portion 113a and is perpendicular to the imaginary surface, inside the corresponding guide hole 114. The spherical portion 113a of each guide pin 113 linearly slides along an inner surface (cam surface) 114a of the guide hole 114 in a direction to separate from the drive shaft 103. When the inclination angle of the swash plate 105 decreases, the spherical portion 113a of each guide pin 113 is rotated counterclockwise as viewed in the drawing about the axis P inside the guide hole 114. The spherical portion 113a of each guide pin 113 linearly slides along the cam surfaces 114a of the guide hole 114 in a direction to approach the drive shaft 103.
That is, the profile of each cam surface 114a is designed such that a path Pxe2x80x2 of the rotary axis P of the corresponding spherical portion 113a is straight.
The graph of FIG. 6 shows the result of an examination on the variable displacement compressor of the above publication performed by the present inventor. As shown by a chain double-dashed line, which is a characteristic line, the present inventor discovered that according to the hinge mechanism 111, or the profile of the cam surface 114a, of the above publication, the top dead center position of each piston 107 fluctuates by a large amount when the displacement is varied.
If the top dead center position of each piston 107 fluctuates, the clearance (top clearance) TC between the piston 107 and the valve plate assembly 109 varies. Therefore, if, for example, the top clearance TC increases by the variation of the displacement, the dead volume of each compression chamber 110 increases. Accordingly, the expansion amount of refrigerant gas increases, which decreases the volumetric efficiency of the variable displacement compressor.
Accordingly, it is an objective of the present invention to provide a variable displacement compressor that includes a hinge mechanism that suppresses fluctuation of a top clearance although the displacement is varied.
To achieve the above objective, the present invention provides a variable displacement compressor, which includes a housing, a single-headed piston, a drive shaft, a rotor, a drive plate, and a hinge mechanism. The housing includes a cylinder bore. The single-headed piston is accommodated in the cylinder bore. The drive shaft is rotatably supported by the housing. The rotor is supported by the drive shaft and rotates integrally with the drive shaft. The drive plate is supported by the drive shaft and slides along and inclines with respect to the drive shaft. The hinge mechanism is located between the rotor and the drive plate. Rotation of the drive shaft is converted into reciprocation of the piston via the rotor, the hinge mechanism, and the drive plate. The hinge mechanism guides the drive plate such that the drive plate slides along and inclines with respect to the drive shaft. The inclination angle of the drive plate determines the displacement of the compressor. The hinge mechanism includes a cam, which is locatedon one of the rotor and the drive plate, and a guide portion, which is located on the other one of the rotor and the drive plate. The cam has a cam surface, which has a predetermined profile. The guide portion abuts against the cam surface. One of the cam surface and the guide portion slides against the other in accordance with inclination of the drive plate. The guide portion traces a path corresponding to the profile of the cam surface with respect to the cam. The path includes a first path corresponding to a small displacement region of the compressor and a second path corresponding to a large displacement region of the compressor. The profile of the cam surface is determined such that the first path and the second path bulge in a direction opposite to each other to compensate for fluctuation of a top dead center position of the piston with respect to the housing.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.